The present invention relates to a steering mechanism with an active force feedback, especially for aircraft. Such a mechanism includes a manually operable steering member for the actuation of the rudder, aileron or elevator components as well as an automatic steering system arranged for cooperation with the manually operable steering member.
Various modifications of such steering mechanism are known in the art. For example, German Patent Publication (DAS) No. 1,053,941 discloses a manual aircraft steering device combined with an automatic steering system, whereby elastic deformations caused by the manual steering lever overcome or at least suppress the stabilizing force of the servo devices. These elastic deformations also displace the manually operable member and generate respective signals which are supplied to the servo system in order to actuate the member to be controlled in accordance with the manually applied muscle power. In this known system the signals are generated only, or rather they become effective only when the force caused by the elastic deformation of the manual steering member has been effective for a sufficient length of time. Thus, in the just mentioned prior art system the cooperation between the manual steering device and the automatic steering system shall be such and the manual control member or stick shall be arranged in such a manner that in response to the application of a sufficient muscle power the stick directly controls or adjusts the member to be controlled, that is, the flap or the rudder. Hence, this type of arrangement does not eliminate the danger of an over control or over steering of the aircraft. Further, the known apparatus has a built in delay between the stick actuation and the response movement of the controlled member because, as mentioned, the signals caused by the elastic deformation become effective only after they have been present for a predetermined length of time. Thus, this known device operates too slow for use in supersonic aircraft.
In order to avoid such delays, German Patent Publication (DOS) No. 2,125,358 suggests a steering mechanism with a metering instrument for sensing the combined effect of the two steering transmission systems and for supplying a signal in the non-mechanical steering system by means of a feedback loop whereby the effect of the mechanical system is neutralized by the effect of the non-mechanical system when the latter is in operation. This known system comprises a control switch for displacing the steering member of the steering system in response to signals of the non-mechanical system. In addition, the mechanical system is directly connected with the control member of the steering mechanism.
In the device according to German Patent Publication (DOS) No. 2,125,358 the mechanical system is continuously connected, however, its effect on the motor or servomotor is eliminated by the effect of the feedback loop. However, when the non-mechanical steering system becomes ineffective, the mechanical steering system is already switched on or rather, in operation so that an effective steering of the motor is assured at all times. However, this type of system cannot prevent that steering impulses caused by the pilot are too large or too quick, thereby causing critical flight conditions.
The steering mechanisms of the above described type or of similar type have been provided with damping means and devices causing an artificial "steering feel", please see for example German Patent Publication (DOS) No. 2,450,158. These devices provide the "steering feel" by means of initial forces or spring forces which the pilot must overcome manually. However, once these initial forces have been overcome, they do not prevent an oversteering of the aircraft.
Summarizing, systems of the prior art substantially operate with control stick forces adjusted to a fixed point or programmed in accordance with the flight range and the aircraft configuration. However, such systems do not take into account the dynamics of the aircraft nor the dynamics of the control or steering mechanism.